Methane is a waste product of the microbial fermentation of animal feed in the forestomach (rumen) of ruminants. Cattle, sheep and goats convert the products of microbial fermentation, for example, acetate, propionate and butyrate, to meat, milk, wool and leather. Inhibition of microbial methane gas production in the rumen can increase the efficiency of production of beneficial animal products.
Fermentation is the result of the collective action of many different genera of microbes, and this collective action produces both waste methane and worthwhile products. One genus of bacteria, Methanobrevibacter, appears to produce all of the methane in the ruminant forestomach. Hence, it is desirable to have an inhibitor of growth of Methanobrevibacter, which would eliminate methane formation and the loss to the atmosphere of about 6 to 13 percent of the energy of animal feed. Conservation of the energy in indispensable products formed by the other rumen microbes would yield greater efficiency of use of animal feed.
Methane produced in domestic ruminants makes a significant contribution to atmospheric methane. Inhibition of its production would also provide an important environmental benefit by eliminating a major contributor to atmospheric warming.
Currently, a variety of compounds is used to increase feed utilization efficiency and decrease methane production. Monensin (U.S. Pat. No. 3,501,568) and lasalocid are ionophore antibiotics used to alter rumen fermentation. Phthalides enhance propionate production and inhibit methane production in the rumen (U.S. Pat. No. 4,333,923). U.S. Pat. No. 4,225,593 describes the use of aplasmomycin, boromycin and acylated and hydrogenated derivatives thereof to modify rumen metabolism in domestic ruminant animals by reducing the proportion of methane formed, and increasing the proportion of propionate at the expense of methane and/or acetate. Heterocyclic trichloromethyl derivatives (U.S. Pat. No. 4,268,510) have also been used to reduce the production of methane during rumen metabolism and increase the formation of propionate at the expense of acetate, and hence improve the animals' rate of growth and their efficiency of feed utilization.
Prior to applicants' discovery, no antibiotics or drugs were known to inhibit the growth of methanogens without concomitantly inhibiting non-methanogens. Thus it is an important feature of the HMG-CoA reductase inhibitors employed in the present invention that they inhibit the growth of methanogens while minimally inhibiting the growth of non-methane-generating microbes. Few of the commonly used antibiotics that inhibit growth of bacteria or fungi inhibit methanogens.
HMG-CoA reductase inhibitors are well known in the pharmaceutical art to treat hypercholesterolemia in humans. They have not, however, been employed in ruminants.
The present invention relates to the novel use of hydroxymethylglutaryl-CoA reductase inhibitors to inhibit the growth of methane-producing bacteria, and in particular to decrease methane production in ruminant animals, thereby improving feed utilization efficiency.